1. Field of the Invention
The present invention relates to electroluminescent lamps. In particular, the present invention relates to electroluminescent lamps having improved interfacial adhesion and improved environmental resistance.
2. Brief Summary of the Related Art
Electroluminescent lamps provide an attractive alternative to conventional lighting systems, especially for display and backlighting devices. An electroluminescent (hereinafter "EL") lamp is electrically similar to a capacitor. A typical EL lamp consists of a dielectric layer and a light-emitting phosphor layer sandwiched between two conductive surfaces, a transparent front electrode and a rear electrode. The primary purpose of the dielectric layer is to allow the lamp to withstand higher voltages without shorting between the conductive surfaces. The phospor layer comprises phosphor particles, typically zinc sulfide or other phosphorescent particles known in the art, suspended in a polymeric matrix. EL lamps illuminate when powered with alternating current (AC-power). As voltage is applied to the conductive surfaces, an electric field is generated across the phosphor and dielectric layers. Twice during each cycle electrons are excited from the valence band into the conduction band. Many of these excited electrons emit light through the transparent front electrodes as they return to their ground state.
One of the major technological barriers to widespread use of EL lamps has historically been their sensitivity to environmental conditions, particularly moisture. As is well-known, phosphor particles degrade in the presence of moisture, and thus must be protected from environmental humidity. One method of protecting phosphor particles has been to shield the particles by encapsulating the EL lamp assembly in a fused, water-resistant poly(chlorotrifluoroethylene) envelope. Another particularly successful method employs microencapsulation of the individual phosphor particles in a glass-like coating, as described in U.S. Pat. Nos. 5,593,782; 5,439,705; and 5,418,062 to Kenton D. Budd and assigned to Minnesota Mining and Manufacturing Company, the relevant portions of which are herein incorporated by reference. While microencapsulation has provided EL lamps with greatly improved resistance to environmental moisture, there still remains a need for additional methods to meet the exacting environmental performance standards required by many users of EL lamps.